A Phase 3 Study of INCA033989 Versus Best Available Therapy in Participants With Essential Thrombocythemia

Inclusion Criteria: * Confirmed diagnosis of high-risk ET. * Presence of mutCALR. * Prior treatment with at least 1 cytoreductive therapy. Exclusion Criteria: * Presence of any hematologic malignancy other than ET. * Major bleeding or thrombosis within the last 3 months prior to study enrollment. * Any prior allogenic or autologous stem-cell transplantation. * Unresolved toxicity ≥ Grade 2 from previous therapy except for stable chronic toxicities (Grade 2) not expected to resolve, such as stable Grade 2 peripheral neuropathy. * Prior nonhematologic malignancy except for the following: Malignancy treated with curative intent and with no evidence of active disease for more than 2 years before screening. Adequately treated carcinoma in situ without current evidence of disease. Other protocol-defined Inclusion/Exclusion Criteria apply.